uniform sampler2D texUnit1;
uniform float pixelOffsetS;
uniform float pixelOffsetT;

void main(void)
{
    vec3 sum = texture2D(texUnit1, gl_TexCoord[0].st + vec2(pixelOffsetS, pixelOffsetT)).rgb;
    sum -= texture2D(texUnit1, gl_TexCoord[0].st).rgb;
    
    gl_FragColor.rgb = vec3(0.299 * sum.r + 0.587 * sum.g + 0.114 * sum.b);
}
